Anisotropic conductive films and coatings generally include an anisotropic non-conductive matrix and conductive particles. The films and coatings can also include adhesives as a non-conductive component. The adhesives typically bind the electrical components in electronic devices, e.g. flip-chips, while the conductive particles dispersed in the adhesive provide a conductive media between the electrical components. Conductive adhesives are typically used as films in the manufacture of devices such as circuit boards and display modules.
In the past, anisotropic conductive films were used in the flat panel display industry to make the electrical and mechanical connections from the drive electronics to the glass substrates of displays. More recently, the films are also being used to make connections between two or more electronic components, such as integrated circuits and circuit boards.
JP 11-135561 discloses an anisotropic conductive adhesive film comprising an elastic conductive particle in a film that consists of a thermosetting adhesive. The diameter of the elastic conductive particle is slightly larger than the thickness of the film of the thermosetting adhesive.
JP 08-007658 discloses an insulating adhesive film in which conductive particulates are uniformly dispersed. The conductive particulates are porous spherical polymer particulates having an average particle diameter of 2 to 20 μm, and are coated with metal.
U.S. Pat. No. 5,636,996 discloses an anisotropic interposer layer comprising a plastic layer (preferably a polyamide polymer) and a plurality of electrically conducting particles disposed in a random pattern throughout the plastic layer. The individual particles extend from one surface of the interposer layer to the other surface, preferably outwardly from the surfaces.
Other anisotropic conductive films have been disclosed that require high temperatures and/or pressures in order to provide adhesion and connection between the layers between which they are interposed. Anisotropic adhesive films have also been disclosed that have a thickness greater than the diameter of conductive particles present in it. The film thickness is reduced only when the layers on either side compress the adhesive film such that the conductive particles come in contact with the layers.
Thus, even though various anisotropic conductive films exist in the art, there is a need for anisotropic conductive films that have a thickness less than the diameter of conductive particles dispersed in them, that can be produced by a simple method, that can be used on flexible substrates, that are compatible with organic conducting materials, and that do not require high temperatures and pressures for providing connection and adhesion. Furthermore, there is a need for anisotropic conductive films that allow the preparation of complex circuitry.